This invention relates to catalysts for the dissociation of methanol to carbon monoxide and hydrogen.
Methanol is a stable, easily stored and handled liquid which can be readily shipped over long distances. It is known that it can be dissociated to synthesis gas by the following reaction: EQU CH.sub.3 OH.fwdarw.CO+2H.sub.2.
The term synthesis gas is generally used to describe various mixtures of carbon monoxide and hydrogen which are useful in a variety of chemical reactions.
The dissociation is usually conducted by contacting the methanol in the vapor phase with a catalyst at temperatures of 200.degree. to 600.degree. C. and pressures from 1 to 50 atmospheres (100 to 5000 kPa). Many catalysts have been disclosed to be useful in the process, i.e., Group VIII metal catalysts, copper-zinc, copper-chromium, copper-nickel, copper-zinc-chromium, copper-chromium-manganese, etc.
For example, U.S. Pat. No. 4,407,238 issued Oct. 4, 1983, discloses a process for the production of hydrogen and carbon monoxide comprising contacting methanol in the vapor phase with a catalyst comprising manganese, copper and chromium. It is taught that this catalyst can be used on a silica support.
Japanese Patent Application 46-49677 published Feb. 28, 1973, claims a copper, chromium, manganese oxide catalyst useful in the manufacture of high purity hydrogen from the reaction of methanol and steam. In an example, the metal oxide catalyst is mixed with about 40% diatomaceous earth prior to reduction with hydrogen and contact with the methanol steam mixture. Use of this catalyst for methanol dissociation without steam is not taught.
U.S. Pat. No. 1,939,708 issued Dec. 19, 1933, discloses a fused catalyst for the gas phase production of methanol and other oxygenated hydrocarbons. The catalyst is the reduction product of a fused mixture of copper oxide, manganese oxide, and an oxide of one of magnesium, aluminum, or silicon.
The melting temperature of these oxides is known to be well over 1000.degree. C. It is also well known in the art that catalysts prepared from fused mixtures have an undesirably low surface area due to the elevated temperatures required for the fusion. See for example Hashimoto, K., et al., Proc. Pac. Chem. Eng. Congr., 3d, Vol. 2, pp. 244-249, Kim, C., et al., Ed., Korean Inst. Chem. Eng., Seoul, S. Korea (1983) for a discussion of the decrease in the surface area of silica-alumina catalysts under conditions of high temperature and steam. Stanislaus, A., et al., Appl. Catal., Vol. 41, 109-119 (1988) disclose that heating Co-Mo/Al.sub.2 O.sub.3 and Ni-Mo/Al.sub.2 O.sub.3 catalysts above 600.degree. C. results in loss of surface area and activity. U.S. Pat. No. 4,420,422 issued Dec. 13, 1983, discloses that solid state firing at temperatures of 600.degree.-1200.degree. C. in the preparation of bismuth pyrochlore results in a surface area lower than that desired.
It is desirable to provide a catalyst which dissociates methanol with high selectivity and high conversion to carbon monoxide and hydrogen. Nonfused catalysts having a higher surface area than fused catalysts generally have greater activity. High selectivity is especially desirable to minimize the formation of unwanted or wasteful by-products.